In the conventional process, the substrate is mounted upon a carbon susceptor and is heated by radio-frequency induction. The vapour-phase reagents are introduced, along with a chemically inert or reducing agent carrier gas--usually hydrogen, which is caused to flow over the surface of the heated substrate. When this process is applied to a number of substrates simultaneously, a high flow-rate is maintained to obviate problems of reagent depletion and to allow the deposition of uniformly thick compound films on the substrate. It is usual to conduct this process at normal pressures. Lower pressure operation is precluded because at such pressures plasma discharge will occur giving rise to reagent disassociation and the deposition of organic material.
Existing commercially available equipment for multi-wafer deposition is complex and expensive, and suffers from major drawbacks. Uniformity in layer thickness, doping and alloy composition is relatively poor and the consumption of reagents is unacceptably high. The use of radio-frequency induction heating requires bulky carbon susceptors, the latter limiting the number and size of substrates that can be used, and also introducing unwanted impurities in the vapour-phase which can become incorporated as undesirable dopants in the deposited film.